1. Field of the Invention
This invention relates to a check valve assembly for controlling the flow of gases or liquids at high pressures, which is particularly well suited for use in high-pressure reciprocating pumps and pressure intensifiers at pressures in excess of 10,000 psi. The check valve assembly is also well suited for handling two-phase fluids, such as slurries, that cause problems with conventional check valves.
2. Description of Prior Art
Check valve assemblies are critical components in high-pressure pumps and pressure intensifiers, because they control the flow of fluid into and out of a pressure chamber which houses the reciprocating plunger. The sealing capability and the reliability of check valves are extremely important factors in the operation of high-pressure pumps, since fluid flow distribution results in disruption of the pump operation. When fluid leakage occurs at the check valve, the pump cannot operate at its designed pressure. Any major failure of the check valve renders a pump useless. A good example is the type of check valve that controls the blood flow in a human heart; failure of the heart valve often results in death.
Today, reciprocating pumps can pressurize working fluids to levels substantially greater than 10,000 psi, at relatively high flow rates. Conventional pressure intensifiers can pressurize a variety of fluids to pressures exceeding 50,000 psi. Such conventional pumps and pressure intensifiers operate at high reciprocating rates and the check valves are therefore subject to tremendously high cyclic stresses. As a result, conventional check valves often fail. Various attempts have been made to improve the design and performance of high-pressure check valves. Unfortunately, further improvements are still necessary.
U.S. Pat. No. 4,412,792 teaches a check valve assembly for use in a hydraulically-driven, double-acting fluid pressure intensifier. The check valve assembly has an inlet check valve and an outlet check valve positioned in a cylindrical valve body that also acts as an end plug for the pressure chamber. The inlet check valve has a machined plate with a smooth mating or sealing surface positioned against the inner surface of the check valve body. The check plate is retained by one or more threaded screws or hollow studs anchored into the check valve body. A spring is used to exert force on the check plate against the check valve body. Thus, the smooth metal-to-metal sealing surface provides fluidic sealing in the inlet check valve assembly. The outlet check valve assembly taught by U.S. Pat. No. 4,412,792 includes a metal or other hard ball or coned poppet which is seated against a tapered mating surface machined in the check valve body, and a backup spacer, or so-called "movable member", instead of a commonly used spring. Such conventional check valve assembly design has several shortcomings. One is the polished metal-to-metal surface sealing that is expensive to achieve due tot he required lapping and is known to have metal fatigue problems with respect tot he check plate, particularly along the edges. A second shortcoming involves the screws and threaded studs that vibrate loose in a pressure-pulsation environment. A loose screw inside the pressure chamber of a pump can result in a disaster. A third shortcoming is the machined check surface of the outlet check valve; such surface is difficult to machine since it is recessed deep inside the check valve body and is difficult to repair. Ball-based check valves are known to have valve seat wear problems due to the thin contact surface between the ball and the coned valve seat. Even slight erosion quickly destroys the entire valve seat. In fact, the valve seat must be made of material softer than the ball in order to obtain a better sealing surface. However, with such arrangement, the useful life of the valve seat can still be a problem due to fluid erosion during valve operation.
U.S. Pat. No. 4,371,001 discloses another check valve assembly that differs slightly from the check valve assembly taught by U.S. Pat. No. 4,412,792, with respect to the components involved. Instead of using a check plate, U.S. Pat. No. 4,371,001 teaches the use of a "valve element" as the inlet check valve and another "valve element" as the outlet check valve. Both "valve elements" are basically flat-surface valve poppets that seat against smooth sealing surfaces. The inlet check valve poppet is retained by a screw, has a plate spring to provide an initial sealing force, and is seated against a smooth inner surface of the check valve body, which also serves as an end plug for a pressure chamber of a fluid pressure intensifier. U.S. Pat. No. 4,371,001 also discloses a removable seating element, shaped as a metal disk having a smooth sealing surface, a cylindrical valve poppet having a smooth sealing surface, and a compression spring used to exert an initial sealing force on the outlet check valve poppet. The outlet check valve seat or disk is retained inside the check valve body with a threaded outlet housing. This particular check valve shares the same shortcomings discussed previously, namely the problems associated with lapped surfaces, a threaded stud positioned inside the pressure chamber, and metal-to-metal fatigue problems. Further, the use of a plate or leaf spring is another shortcoming due to the very limited travel distance and a peculiar pivoting motion that such plate spring provides to the inlet check valve poppet. As a result, the inlet check valve poppet is prone to premature edge failure and the sealing surface of the check valve body can be gouged by the valve poppet. The outlet check valve assembly taught by U.S. Pat. No. 4,371,001 also has a very limited fluid passage.
U.S. Pat. No. 4,716,924 teaches a replaceable discharge valve assembly for a high-pressure reciprocating plunger pump having a generally tubular valve seat designed to mate with a reciprocating valve closure member. One set of such valve assemblies serves as the in inlet check valve for the pressure chamber while another set of such valve assemblies serves as the outlet check valve for the same pressure chamber that houses a reciprocating pump plunger. A cylindrical valve poppet having guide ribs and a tapered sealing surface is used to engage the sealing surface of the tubular valve seat. The inlet and outlet check valves are designed similarly but differ in size and a re positioned in separate cylindrical bores within a steel block. Such check valve assemblies are quite commonly used in conventional crankshaft plunger pumps, all having hardened steel valve poppets and valve seats with tapered, smooth mating surfaces. Some conventional pumps are very large and have relatively large valve poppets that produce significant pounding forces when the valve poppet closes against the valve seat. Furthermore, the valve sealing surface is also exposed to high-velocity fluid flow whenever the valve poppet opens. As a result, the valve mating surfaces wear out rapidly and thus require frequent replacement of both the valve poppet and the valve seat.
U.S. Pat. No. 4,862,911 teaches a check valve assembly that combines inlet and outlet check valves in a single valve body that can be housed inside a high-pressure cylinder that acts as a pressure chamber of a pump or pressure intensifier. A threaded hollow stud serves as a retainer for both inlet and outlet check valves. The valve elements comprise balls, flat disks, or coned poppets. The basic sealing surfaces form metal-to-metal seals, and thus have all of the inherent problems, such as a requirement for precision machining, lapping, or both, metal fatigue problems, metal deformation problems, metal erosion problems, and inherently poor fluidic seals resulting from metal-to-metal surface contact.
This invention solves such problems associated with conventional check valve assemblies without sacrificing pressure and flow capabilities or convenience during use.